Climate change, including ocean acidification (OA), represents a major threat to coral-reef ecosystems. Although previous experiments have shown that OA can negatively affect the fitness of reef corals, these have not included the long-term effects of competition for space on coral growth rates. Our multispecies year-long study subjected reef-building corals from the Gulf of Aqaba (Red Sea) to competitive interactions under present-day ocean pH (pH 8.1) and predicted end-of-century ocean pH (pH 7.6). Results showed coral growth is significantly impeded by OA under intraspecific competition for five out of six study species. Reduced growth from OA, however, is negligible when growth is already suppressed in the presence of interspecific competition. Using a spatial competition model, our analysis indicates shifts in the competitive hierarchy and a decrease in overall coral cover under lowered pH. Collectively, our case study demonstrates how modified competitive performance under increasing OA will in all likelihood change the composition, structure and functionality of reef coral communitie

Light-induced tunable photonic systems are rare in nature, and generally beyond the state-of-the-art in artificial systems. Sapphirinid male copepods produce some of the most spectacular colors in nature. The male coloration, used for communication purposes, is structural and is produced from ordered layers of guanine crystals separated by cytoplasm. It is generally accepted that the colors of the males are related to their location in the epipelagic zone. By combining correlative reflectance and cryoelectron microscopy image analyses, together with optical time lapse recording and transfer matrix modeling, it is shown that male sapphirinids have the remarkable ability to change their reflectance spectrum in response to changes in the light conditions. It is also shown that this color change is achieved by a change in the thickness of the cytoplasm layers that separate the guanine crystals. This change is reversible, and is both intensity and wavelength dependent. This capability provides the male with the ability to efficiently reflect light under certain conditions, while remaining transparent and hence camouflaged under other conditions. These copepods can thus provide inspiration for producing synthetic tunable photonic arrays.

Coral reefs are deteriorating at alarming rates, with coral disease outbreaks increasing in prevalence and in space. Anomalously high ocean temperatures are thought to significantly contribute to this problem. We collected a unique and highly resolved dataset of a White Plague Disease (WPD) outbreak from the coral reef of Eilat (Israel, Red Sea). By fitting a novel epidemiological model to the data, we characterize the dynamics of WPD, and study the possible effects of future increasing sea-surface temperatures (SST) on disease dynamics. In contrast to earlier studies, our approach captures the dynamics of coral disease both in space and time, and accounts for the highly seasonal nature of the annual outbreaks. We also apply a novel combination of spatiotemporal statistics and null hypothesis approaches to study the disease progression. Model forecasts into the future show that for some scenarios even an increase of only 0.5°C in SST can cause epidemics to double in magnitude. Since the probability of infection is found to be negatively associated with coral density, this implies that the spatial nature of disease transmission can both enhance and restrict the magnitude of annual epidemics. The results have implications for designing management policies appropriate for coral reef conservation.

Microscopic-scale processes significantly influence benthic marine ecosystems such as coral reefs and kelp forests. Due to the ocean’s complex and dynamic nature, it is most informative to study these processes in the natural environment yet it is inherently difficult. Here we present a system capable of non-invasively imaging seafloor environments and organisms in situ at nearly micrometre resolution. We overcome the challenges of underwater micro-scopy through the use of a long working distance microscopic objective, an electrically tunable lens and focused reflectance illumination. The diver-deployed instrument permits studies of both spatial and temporal processes such as the algal colonization and overgrowth of bleaching corals, as well as coral polyp behaviour and interspecific competition. By enabling in situ observations at previously unattainable scales, this instrument can provide important new insights into micro-scale processes in benthic ecosystems that shape observed patterns at much larger scales.

Events of mass coral bleaching and mortality have increased in recent decades worldwide, making coral recruitment more important than ever in sustaining coral-reef ecosystems and ensuring their resilience. During the last four decades, the coral reefs of Eilat have undergone severe deterioration due to both anthropogenic and natural causes. Recruitment failure has been frequently suggested as one of the main mechanisms underlying this deterioration. Here we assess the demographic replenishment and resilience potential of the local reefs, i.e., the potential for new sexually derived corals to recruit and exceed the community’s mortality rate. We present a detailed analysis of coral community demography, obtained by means of high-resolution photographic monitoring of permanently marked plots. Coral spats as small as 1 mm were documented and the detailed dynamics of coral recruitment and mortality were recorded, in addition to other common ecological measurements. The cumulative quantity of recruited individuals was twofold to fivefold higher than total mortality. The most significant predictor variable for coral recruitment among all ecological parameters measured was the available substrate for settlement, and the survival of recruited corals was correlated with reef structural complexity. Two consecutive annual reproductive seasons (June–September of each year) with high recruitment rates were monitored. Combined with the high survival of recruits and the increase in coral live cover and abundance, the findings from this study indicate an encouraging potential for recovery of these reefs.

Coral Reefs: 2016

Hydrodynamic constraints of suction feeding in low Reynolds Numbers, and the critical period of larval fishes

Larval fishes suffer prodigious mortality rates, eliminating 99% of the cohort within a few days after their first feeding. Hjort (1914) famously attributed this "critical period" of low survival to larval inability to obtain sufficient food. We discuss recent experimental and modeling work, suggesting that the viscous hydrodynamic regime have marked effects on the mechanism of suction feeding in larval fish. As larvae grow, the size of the gape and associated volume of

the mouth increase. At the same time, larvae swim faster and can generate faster suction flows, thus transiting to a hydrodynamic regime of higher Reynolds numbers. This hydrodynamic regime further leads to changes in the spatio-temporal patterns of flow in front of the mouth, and an increasing ability in larger larvae to exert suction forces on the prey. Simultaneously, the increase in swimming speed and the distance from which the prey is attacked result in higher

rates of encountering prey by larger (older) larvae. In contrast, during the first few days after feeding commence the lower rates of encounter and success in feeding translate to low feeding rates. We conclude that young larvae experience ‘‘hydrodynamic starvation,’’ in which low Reynolds numbers mechanically limit their feeding performance even under high densities of prey.

Integrative and Comparative Biology: 2015

DOI: 10.1093/icb/icv030

Evidence for rhythmicity pacemaker in the calcification process of scleractinian coral

1Bar Ilan University, Israel

2Institute of Paleobiology, Poland

3Sorbonne Universités, Muséum National d’Histoire Naturelle, France

4Weizmann Institute of Science, Israel

5School of Architecture, Civil and Environmental Engineering (ENAC), Switzerland; and University of Lausanne, Switzerland

Scientific Reports: 2016

doi:10.1038/srep20191

Reef-building scleractinian (stony) corals are among the most efficient bio-mineralizing organisms in nature. The calcification rate of scleractinian corals oscillates under ambient light conditions, with a cyclic, diurnal pattern. A fundamental question is whether this cyclic pattern is controlled by exogenous signals or by an endogenous ‘biological-clock’ mechanism, or both. To address this problem, we have studied calcification patterns of the Red Sea scleractinian coral Acropora eurystoma with frequent measurements of total alkalinity (AT) under different light conditions. Additionally, skeletal extension and ultra-structure of newly deposited calcium carbonate were elucidated with 86Sr isotope labeling analysis, combined with NanoSIMS ion microprobe and scanning electron microscope imaging. Our results show that the calcification process persists with its cyclic pattern under constant light conditions while dissolution takes place within one day of constant dark conditions, indicating that an intrinsic, light-entrained mechanism may be involved in controlling the calcification process in photosymbiotic corals.

A quick, easy and non-intrusive method for underwater volume and surface area evaluation of benthic organisms by 3D computer modeling

1. In order to understand physiological, ecological and biological processes, it is often crucial to determine an organism's volume and surface area (SA). Most of the available methods require sacrificing the organism or at least removing it from its natural habitat, in order to measure these parameters. Advances in computer vision algorithms now allow us to determine these parameters using non-destructive, three-dimensional modelling. The addition of cloud computing and the availability of freeware make this tool widely accessible.

2. Photographs of corals and sponges were taken in natura and used to create digital 3D models using the ‘structure-from-motion’ technique. Modelling was done online using 123D Catch freeware (Autodesk Inc.). Volume and SA of the corals and sponges were calculated from these 3D models.

3. Comparing in situ 3D modelling to current measuring methods (e.g. water displacement, paraffin dipping) showed that volume calculation by 3D modelling gave fast results accurate to within 8% of estimated true volume. Using cloud computing enabled the creation of a 3D model in <30 min. SA accuracy was found to differ significantly, depending on the shape of the modelled object, with an accuracy ranging widely from 2% to 18%.

4. We found that in situ volume and SA measurements created by 3D modelling enable easy, fast and non-intrusive studies of benthic aquatic organisms, without removing the subject organisms from their habitat, thus enabling continuous study of natural growth over extended time periods. The freely available freeware, along with ease of use, makes this method accessible to many areas of research.

Structural basis for the brilliant colors of the sapphirinid copepods

1Departments of †Structural Biology and ‡Physics of Complex Systems, Weizmann Institute of Science

2Departments of †Structural Biology and ‡Physics of Complex Systems, Weizmann Institute of Science

3The Interuniversity Institute for Marine Sciences in Eilat

Males of sapphirinid copepods use regularly alternating layers of hexagonal-shaped guanine crystals and cytoplasm to produce spectacular structural colors. In order to understand the mechanism by which the different colors are produced, we measured the reflectance of live individuals and then characterized the organization of the crystals and the cytoplasm layers in the same individuals using cryo-SEM. On the basis of these measurements, we calculated the expected reflectance spectra and found that they are strikingly similar to the measured ones. We show that variations in the cytoplasm layer thickness are mainly responsible for the different reflected colors and also that the copepod color strongly depends on the angular orientation relative to the incident light, which can account for its appearance and disappearance during spiral swimming in the natural habitat.

J. Am. Chem. Soc.: 2015

DOI: 10.1021/jacs.5b05289

Benthic response to removal of fish cages

For about 20 years, finfish were reared in floating cages at the northern end of the Gulf of Aqaba-Eilat, Red Sea. The benthic ecosystem at the fish cages area was severely impacted by organic enrichment, resulting in an environment with no living foraminifera. A government decision led to the fish cages' removal in June 2008, creating a unique opportunity to monitor and assess post-removal changes in the benthos. Three years of benthic foraminiferal assemblage monitoring, beginning in July 2008 and ending in July 2011, are summarized.

Zooplankton May Serve as Transmission Vectors for Viruses Infecting Algal Blooms in the Ocean

Marine viruses are recognized as a major driving force regulating phytoplankton community composition and nutrient cycling in the oceans. Yet, little is known about mechanisms that influence viral dispersal in aquatic systems, other than physical processes, and that lead to the rapid demise of large-scale algal blooms in the oceans. Here, we show that copepods, abundant migrating crustaceans that graze on phytoplankton, as well as other zooplankton can accumulate and mediate the transmission of viruses infecting Emiliania huxleyi, a bloom-forming coccolithophore that plays an important role in the carbon cycle. We detected by PCR that >80% of copepods collected during a North Atlantic E. huxleyi bloom carried E. huxleyi virus (EhV) DNA. We demonstrated by isolating a new infectious EhV strain from a copepod microbiome that these viruses are infectious. We further showed that EhVs can accumulate in high titers within zooplankton guts during feeding or can be adsorbed to their surface. Subsequently, EhV can be dispersed by detachment or via viral-dense fecal pellets over a period of 1 day postfeeding on EhV-infected algal cells, readily infecting new host populations. Intriguingly, the passage through zooplankton guts prolonged EhV’s half-life of infectivity by 35%, relative to free virions in seawater, potentially enhancing viral transmission. We propose that zooplankton, swimming through topographically adjacent phytoplankton micropatches and migrating daily over large areas across physically separated water masses can serve as viral vectors, boosting host-virus contact rates and potentially accelerating the demise of large-scale phytoplankton blooms.

The phenomenon of coral fluorescence in mesophotic reefs, although well described for shallow waters, remains largely unstudied. We found that representatives of many scleractinian species are brightly fluorescent at depths of 50–60 m at the Interuniversity Institute for Marine Sciences (IUI) reef in Eilat, Israel. Some of these fluorescent species have distribution maxima at mesophotic depths (40–100 m). Several individuals from these depths displayed yellow or orange-red fluorescence, the latter being essentially absent in corals from the shallowest parts of this reef. We demonstrate experimentally that in some cases the production of fluorescent pigments is independent of the exposure to light; while in others, the fluorescence signature is altered or lost when the animals are kept in darkness. Furthermore, we show that green-to-red photoconversion of fluorescent pigments mediated by short-wavelength light can occur also at depths where ultraviolet wavelengths are absent from the underwater light field. Intraspecific colour polymorphisms regarding the colour of the tissue fluorescence, common among shallow water corals, were also observed for mesophotic species. Our results suggest that fluorescent pigments in mesophotic reefs fulfil a distinct biological function and offer promising application potential for coral-reef monitoring and biomedical imaging.

PLos One: 2015

DOI: 10.1371/journal.pone.0128697

Breakdown of coral colonial form under reduced pH conditions is initiated in polyps and mediated through apoptosis

Certain stony corals can alternate between a calcifying colonial form and noncalcifying solitary polyps, supporting the hypothesis that corals have survived through geologic timescale periods of unfavorable calcification conditions. However, the mechanisms enabling this biological plasticity are yet to be identified. Here we show that incubation of two coral species (Pocillopora damicornis and Oculina patagonica) under reduced pH conditions (pH 7.2) simulating past ocean acidification induce tissue-specific apoptosis that leads to the dissociation of polyps from coenosarcs. This in turn leads to the breakdown of the coenosarc and, as a consequence, to loss of coloniality. Our data show that apoptosis is initiated in the polyps and that once dissociation between polyp and coenosarc terminates, apoptosis subsides. After reexposure of the resulting solitary polyps to normal pH (pH 8.2), both coral species generated coenosarc tissues and resumed calcification. These results indicate that regulation of coloniality is under the control of the polyp, the basic modular unit of the colony. A mechanistic explanation for several key evolutionarily important phenomena that occurred throughout coral evolution is proposed, including mechanisms that permitted species to survive the third tier of mass extinctions.

Journal of the Marine Biological Association of the United Kingdom: 2017 (DOI:10.1017/S0025315416002022)

Abstract:

Christmas tree worms (Spirobranchus spp.) are prominent sessile organisms inhabiting hermatypic corals in tropical and subtropical reefs. Until recently, most of the larger Spirobranchus species were considered to be in obligatory associations with live hermatypic corals. However, recent studies indicate that some Spirobranchus species can build tubes on artificial substrate as well and that others may show preferences for using specific species of corals and hydrozoans as substrates. In the present study, we conducted a survey of Spirobranchus spp. substrate preference in the Gulf of Eilat. We found seven morphotaxa of Spirobranchus, of which two may be a single new species. We show that Spirobranchus taxa differ not only in their morphology, but also in their substrate use. Our results demonstrate that the ecological niche of Spirobranchus is species-specific, and a putative innate preference exists for some substrates.

Effect of oxygen on coral fanning by mutualistic fish

Coral branches partially block the flow of water through the colony, creating an inner zone of reduced water exchange where hypoxic conditions can develop during the night. Previous studies have shown that this oxygen deficiency is alleviated by the fanning behavior of mutualistic damselfish that spend the night between the coral branches, constantly moving their fins. Our findings show that fin-stroking frequency during fanning by the damselfish Dascyllus marginatus is moderately plastic, with lower frequency under higher oxygen concentration, and vice versa. The inter-play between oxygen concentration and fin motion maintains nearly steady oxygen concentration between the coral branches during the night.

Superoxide in seawater may be produced by heterotrophic bacteria, with implications for trace metal cycling in the sea

In the past decade, sensitive analytical techniques have enabled a new look at the distributions, sources and chemical reactivity of superoxide (O2 −) in the ocean. Until recently superoxide was thought to form solely through photochemical reactions in the surface ocean, but now biological processes are considered to be equally important in generating superoxide. Diaz et al. (1) show that heterogeneous bacteria produce superoxide and potentially represent a substantial source of superoxide in the sea.

The Gulf of Eilat offers refugium for coral reefs in an era of climate change

Maoz Fine, Hezi Gildor and Amatzia Genin
Faculty of Life Sciences, Bar Ilan University; Dept. of Earth Sciences, The Hebrew University of Jerusalem and The Interuniversity Institute of Eilat

The stability and persistence of coral reefs in the decades to come is uncertain due to global warming and repeated
bleaching events that will lead to reduced resilience of these ecological and socio-economically important ecosystems.
Identifying key refugia is potentially important for future conservation actions. We suggest that the Gulf of Aqaba
(GoA) (Red Sea) may serve as a reef refugium due to a unique suite of environmental conditions. Our hypothesis is
based on experimental detection of an exceptionally high bleaching threshold of northern Red Sea corals and on the
potential dispersal of coral planulae larvae through a selective thermal barrier estimated using an ocean model. We
propose that millennia of natural selection in the form of a thermal barrier at the southernmost end of the Red Sea
have selected coral genotypes that are less susceptible to thermal stress in the northern Red Sea, delaying bleaching
events in the GoA by at least a century.

Stinging Cell Mechanism

Tamar Lotan
Marine Biology Department, The Leon H.Charney School of Marine Sciences, University of Haifa

The Cnidarians' (jellyfish, coral, sea anemone, hydra) stinging cells manufacture intracellular structures known as cnidocysts, cyst capsules, equipped with an injection system and act as biological syringes. These capsules contain highly folded thin tube resembling a needle and can hold pressure of 150 bar. Upon activation the tube unfolds and penetrates its target at a remarkable acceleration of 5•106g to deliver 10 times capsule volume through the needle. We have shown that isolated capsules can be used to actively deliver drug solutions to the skin. Since the mechanisms of both needle release and fluid injection are flow driven, we are studying flow and transport processes in these natural injectors. We are also interested in understanding the biological assembly of the capsule and its evolutionary origin.

Ellie Foran, Maoz Fine
The Interuniversity Institute for Marine Sciences of Eilat and Faculty of Life Scieces, Bar Ilan University

A Scanning Electron Microscopy (SEM) image shows the composition of fish-gut pellets at a
microscopic level. Photo by E. Foran

Marine fish create a soft, disordered form of calcium carbonate (CaCO3) in their intestines, which easily dissolve when excreted in seawater. In a collaborative effort, scientists from Bar-Ilan University, the Interuniversity Institute of Marine Sciences in Eilat and the Weizmann Institute investigated some of the fundamental characteristics of calcium carbonate (CaCO3) minerals found in fish guts, which function as a reverse sponge for water absorption in the intestine. Results of the study, published in the journal Scientific Reports, revealed the piscine pellets analyzed were amorphous calcium carbonate (ACC), the most soluble of all CaCO3 forms. It was first suspected that the intestinal deposits were made up of something other than a crystalline structure, based on the malleable material, difference in pellet shape, and mucus covering. In addition, more and more ACC examples were being found among eclectic groups of organisms. So why not in fish guts? Experiments performed on the gilt-head seabream confirmed this hypothesis, also showing that the mineral remained in this soft, amorphous state throughout the intestinal tract. The researchers attribute the mineral’s stability, in part to the substantial incorporation of magnesium ions, originating from ingested seawater.

The extent of this stability was tested when fish carbonates were placed in seawater and monitored for dissolution. Rather than immediately crystallize, the pellets dissolved within an hour, nearly doubling the carbonate ion concentration in the surrounding water.

If fish regularly add very soluble carbonate to the sea, they may be important contributors to local environments, such as coral reefs, that use available carbonate to build skeletons.

Active centering of dust by puff-shaped natural Trichodesmium colonies, enabling them to dissolve and acquire iron from dust.

Iron is recognized as a major limiting element for marine primary producers and as such affects global carbon cycling and the world climate. Trichodesmium is a globally important marine N2 fixing cynobacterium that fuels other phytoplankton with new nitrogen sources. Trichodesmium has high requirement for iron but it resides in iron poor water. Dust deposited on the ocean surface was suggested as a possible source of iron for Trichodesmium. In a recent study published in Nature Geosciences (Rubin et al. 2011) we explored the sequence of steps by which natural and cultured Trichodesmium collect, process and utilize iron from synthetic iron oxides and desert dust. We discovered that Trichodesmium efficiently traps dust in its intricate colony morphology and that it can actively shuttle dust particles from the colony periphery to its core. This fascinating phenomenon enables it to keep the dust in the colony core and extract nutrient elements such as iron from the dust.

Dispersal of coral-reef fishes in the northern Gulf of Aqaba

Naama Kimmerling, Moshe Kiflawi
The Interuniversity Institute for Marine Sciences of Eilat and Ben Gurion University of the Negev

Photo: Meytal Markovich

The life-cycle of most coral-reef fish species consists of an adult stage, which is bound to a local reef, and a pelagic larval stage which is spent in the open sea. Dispersal in these fishes is limited to the larvae, making the pelagic stage a key demographic and ecological player. Our lab is currently focusing on two questions relating to the pelagic stage. First, using intensive field samples and biophysical models, we are trying to identify the factors that affect the spatial and temporal distribution of the larvae, and how it may ultimately affect dispersal trajectories in the Gulf of Eilat/Aqaba. Second, using in-situ experimentation, we are trying to uncover the orientation capabilities of these tiny larvae; with emphasis on their use of a sun compass.

Decision-making by cleaner-wrasse

Ofri Mann, Moshe Kiflawi
The Interuniversity Institute for Marine Sciences of Eilat and Ben Gurion University of the Negev

The text-book example of inter-specific mutualism must be the relationship between the cleaner wrasse and their clients; whereby clients benefit from having their ecto-parasites removed and the cleaners gain a meal. The system presents an interesting model for addressing questions related to the decision-making and market-dynamics (i.e. supply and demand). We are currently combining theoretical and field/lab work to examine optimal ‘cleaning-bout' durations for a cleaners operating either alone or as part of a cooperating pair.

Evidence for submesoscale barriers to horizontal mixing in the ocean from current measurements by HF radar

Numerous recent studies have investigated ocean mixing on mesoscales or larger scales using velocity fields derived from drifters, numerical models, and observations from satellites. These studies demonstrate the non-uniform characteristics of mixing and the existence of coherent structures.

Unlike these previous studies, we concentrate on the submesoscale (~1-20 km) motions leading to horizontal mixing. Accurate parameterizations of submesoscale mixing processes are critical in simulating and predicting ocean circulation and changes in the climate. Due to limited computer power, present day ocean and climate models resolve processes on scales down to a few tens of km. The combined effect of sub-grid processes, including different types of instabilities and waves, has to be parameterized, and this is typically done using diffusion-like parameterizations, with an "eddy diffusivity" which is larger than molecular diffusivity, but which implies similar physical characteristics to that of molecular diffusion. Two implications to using homogeneous (or even just smoothly varying) "eddy diffusivity" are that first, there are no barriers to mixing, and second, that the average absolute dispersion of particles (i.e. the average displacement of particles from their origins) grows in proportion to the square root of time. (Roughly speaking, by barrier we mean a line that separates regions with different mixing characteristics, and with little mixing across this line.)

Using a dataset of surface currents that collected in the Gulf of Eilat by HF radar, at an unprecedented combination of long duration (over four years) and high resolution (300 m), we have been investigating the horizontal mixing on the scale of a few km. Our study yielded important, unexpected results. We demonstrate, experimentally, the complexity of ocean mixing on such small scale and the existence of temporary barriers to mixing. This has important implications for the dispersion of pollutants, nutrients, larvae, etc., and therefore for a wide range of predictions. We were able to also verify the existence of these barriers for the first time by aerial-photographs (Figure 1). The existence of such barriers requires a new approach to the way mixing is parameterized in ocean and climate models.

Figure 1. Left: Relative dispersion in the Gulf of Eilat based on 36 hours of virtual particle tracking simulation using the measured HF radar surface velocities on February 3, 2006. The light-colored lines with higher relative dispersion values divide the domain into relatively well mixed regions, but little mixing occurs across these lines that therefore serve as barriers to mixing. Note the high relative dispersion line (between the red arrows) that starts in the western side of the northern coast and ends on the eastern coast. White areas are regions from which particles have moved out of the domain. Right: An aerial-photograph of the Gulf on Feb 5, after a flood washed sediments into the ocean. Note that the sediments do not mix across the same barrier line that was calculated from the currents observed by the HF radar and shown on the left. For orientation, note that the green rectangle both panels marks the same location.

The great benefit of pulsation in soft corals

Amatzia Genin, Maya Kremien, Uri Shavit, and Tali Mass
The Interuniversity Institute for Marine Sciences and The Hebrew University of Jerusalem (AG, MK and TM) and The Technion, Israel Institute of Technology, Haifa (US)

The Xeniid coral Heteroxenia fuscescens during pulsation (A) and rest (B). Note the different postures of the tentacles among the pulsating polyps, demonstrating the absence of phase synchronization among the polyps within the colony. (C) - A schematic illustration of the stem and tentacles of a single polyp.

Soft corals of the family Xeniidae exhibit a unique, rhythmic pulsation of their tentacles (see http://piv.technion.ac.il/Research/Hetroxenia/Pulsating.mp4), first noted by Lamarck nearly 200 years ago. Yet, the adaptive benefit of this perpetual, energetically-costly motion is poorly understood. Using in-situ Underwater Particle Image Velocimetry we found that the pulsation motions thrust water upward and enhance mixing across the coral-water boundary layer. The induced upward motion effectively prevents re-filtration of water by neighboring polyps, while the intensification of mixing, together with the upward flow, greatly enhances the coral’s photosynthesis. A series of controlled laboratory experiments with the common xeniid coral Heteroxenia fuscesens showed that the net photosynthesis rate during pulsation was up to an order of magnitude higher than during the coral’s resting, non-pulsating state. This enhancement diminished when the concentration of oxygen in the ambient water was artificially raised, indicating that the enhancement of photosynthesis was due to a greater efflux of oxygen from the coral tissues. By lowering the internal oxygen concentration, pulsation alleviates the problem of reduced affinity of RuBisCO to CO2 under conditions of high oxygen concentrations. The photosynthesis-respiration ratio of the pulsating H. fuscesens was markedly higher than the ratios reported for non-pulsating soft and stony corals. While pulsation is commonly used for locomotion and filtration in marine mobile animals, its occurrence in sessile (bottom attached) species is limited to members of the ancient phylum Cnidaria, where is it used to accelerate water and enhance physiological processes.